What do you think of Class D amplifiers?

[NHL]

It is quite interesting to read the Icepower history, available on their homepage. The field was left wide open by the conservative designers. The initial offerings were 1000 watt active speakers, to make the public take notice. Todays 50 watt class D amps seems to be a little bit sulten.

 

[tino]

Following Devialet's lead ... seems like a there could be a few more esoteric Class D amplifiers on their way this year ... I like the look of this one ... the Intuition from Wadia ...

http://www.youtube.com/watch?v=opYOkaXsC3c&NR=1

http://www.monoandstereo.com/2013/01/wadia-intuition-01.html

The big display reminds me of Roksan/Artora Oxygene and Resolution Cantata.

Specs are 350W into 4ohm, analogue and digital (inc. USB) inputs.

 

[Frank Harvey]

I think most manufacturers will be developing their own at the moment as the government is bound to bring in laws relating to power usage at some point in the near future - the 'less than 1W in standby' thing is just the start...

 

[Singslinger]

Used to own a Jeff Rowland Continuum 500 integrated, class D design. When idling, it ran quite hot so maybe class D isn't that environmentally friendly. Didn't quite like the sound - not enough body. Give me class A any day.

 

[busb]

I've lived with my Primare A34.2 power amp for nearly a month. It has a brighter presentation than I'm used to. Decent recordings sound amazing - fabulous bass control, incredible levels of detail, imaging breathtaking with pretty clean treble. Given a poor recording, you know it all too soon. Most, if not all classical music sounds great but much pop sounds dire so this amp takes no prisoners, none, zilch! How close it sounds to other class D amps, I just don't know. I'd speculate that some would love the sound but others would prefer a more even-handed approach with less detail of the warts being a price worth paying.

 

[BigColz]

I've lived with my Primare A34.2 power amp for nearly a month. It has a brighter presentation than I'm used to. Decent recordings sound amazing - fabulous bass control, incredible levels of detail, imaging breathtaking with pretty clean treble. Given a poor recording, you know it all too soon. Most, if not all classical music sounds great but much pop sounds dire so this amp takes no prisoners, none, zilch! How close it sounds to other class D amps, I just don't know. I'd speculate that some would love the sound but others would prefer a more even-handed approach with less detail of the warts being a price worth paying.

It's definatly a tough balance.. I had £3k Cyrus pre/power before and the right recording sounded good but even then the top end was way to much for loud listening.. The second you had a bad or bright recording it became unbearable.. The anylitical nature also made it fatiguing and hard to let the music flow.. My new amp is an absolute gem.. Theres just as much detail but you can choose whether to pick it out or just let it flow. Extremely musical and very slightly warm. I found Electro's quite different from other class D's and will keep this one for a few years before doing a big step up. Then will try valve/class a/hybrids but for now i'm very happy. Maybe you should give them an audition

 

[AlmaataKZ]

I heard them only once - the sound was fantastic. I was also impressed with how small they are and the efficiency figures are great. Here is the set-up I heard (the amps are the small blue boxes near the speakers. I do not remember what make and wattage they were but someting incredibly high - 500W each? ):

What's not to like? I also think class D will become more common.

As a side-though: the boxes are so small that is very natural to want to build them into the speaker box. and the next step from there is, naturally, an active crossover ;-)

 

[busb]

I heard them only once - the sound was fantastic. I was also impressed with how small they are and the efficiency figures are great. Here is the set-up I heard (the amps are the small blue boxes near the speakers. I do not remember what make and wattage they were but someting incredibly high - 500W each? ):

What's not to like? I also think class D will become more common.

As a side-though: the boxes are so small that is very natural to want to build them into the speaker box. and the next step from there is, naturally, an active crossover ;-)

Despite my reservations regarding my current amp, I've no doubt that class D will replace class AB amps in the next 10 years, perhaps sooner. Unless legislation intervenes, class D will be the most common, followed by class A & valve

 

[JMacMan]

Properly executed and implemented, I see no tecnical reason why a low distortion Class D design cannot be at least as good, if not better than other amplification designs, on sonic terms especially given the sheer minimum of devices in the signal path involved, compared to other amplfication technologies.

I've heard various so called high end amps; a Naim 552/500, Gryphon, Krell, McIntosh, Conrad-Johnson, Audio Research, Bryston, Quad et al, and would not swap out my Class D TA-DA9000ES Sony amp for any of them in the context of a passive separates system, and where sound quality overall was the final arbiter.

John

 

[andyjm]

There are probably more class D amplifiers (in mobile phones) built in a year than any other type of amp, yet the high end hifi industy struggles to drag itself into the 21st century where class D is still perceived as a novel and scary amplifier topology.

Given that the input signal is (in most cases) a time series of samples, not an analogue waveform, it makes perfect sense to keep the signal digital until the final driver stage - if anything it is more bizzare to convert the signal to analogue halfway through the chain and use an analogue amplifier.

High quality, low cost, efficient class D allows multiple amps to be mounted within a speaker enclosure, with the all the benefits of active digital crossovers. My humble Squeezebox Boom has a DSP crossover, 6 channels of class D amplification with each speaker driver having a separate amp and the headphone output having two separate amps of its own. All of this, a display driver and streamer on a circuit board about 3 inches square.

Many (most?) subs are already class D with the amp in the enclosure. Pro monitors are well down this route. I look forward to the Focal / Naim partnership bringing out a range of active digital speakers to show how it can be done for domestic use at hopefully a reasonable price.

A clean and efficient solution. No need for DACs, speaker cables, amps - what will we talk about?

 

[jcbrum]

There are probably more class D amplifiers (in mobile phones) built in a year than any other type of amp, yet the high end hifi industy struggles to drag itself into the 21st century where class D is still perceived as a novel and scary amplifier topology.

Given that the input signal is (in most cases) a time series of samples, not an analogue waveform, it makes perfect sense to keep the signal digital until the final driver stage - if anything it is more bizzare to convert the signal to analogue halfway through the chain and use an analogue amplifier.

Er, hang on, . . . Class D amplifiers are analogue devices, not digital.

High quality, low cost, efficient class D allows multiple amps to be mounted within a speaker enclosure, with the all the benefits of active digital crossovers.

Sure, you can use both digital and analogue technologies in the same box if you wish, but you would have to provide multiple DACs as well, to convert the digital signal channels from the digital crossovers to feed the analogue Class D amplifiers. There is no correlation between DSP and Class D amps.

I look forward to the Focal / Naim partnership bringing out a range of active digital speakers to show how it can be done for domestic use at hopefully a reasonable price.

A clean and efficient solution. No need for DACs, speaker cables, amps - what will we talk about?

Loudspeakers must always contain an analogue tranducer, that's how they work, - your ears are analogue. If you provide a digital signal source, then you must use a DAC to drive the analogue transducer.

JC

 

[Andrew Everard]

FWIW, and only sightly OT, I'm currently playing with some little Class T stereo power amps from Trends Audio, controlled by a valve hybrid preamp, and so far liking what I hear (as a desktop system, at least).

Will report more fully in some bloggage at a later date, when I have spent more time with them.

 

[shooter]

I have Class D diving the woofers and cant say that they sound different to any other woofer i've heard.

Highly efficient with high power output, whats not to like? Partner with suitable speakers and/or pre and you have a nice system.

 

[andyjm]

There are probably more class D amplifiers (in mobile phones) built in a year than any other type of amp, yet the high end hifi industy struggles to drag itself into the 21st century where class D is still perceived as a novel and scary amplifier topology.

Given that the input signal is (in most cases) a time series of samples, not an analogue waveform, it makes perfect sense to keep the signal digital until the final driver stage - if anything it is more bizzare to convert the signal to analogue halfway through the chain and use an analogue amplifier.

Er, hang on, . . . Class D amplifiers are analogue devices, not digital.

High quality, low cost, efficient class D allows multiple amps to be mounted within a speaker enclosure, with the all the benefits of active digital crossovers.

Sure, you can use both digital and analogue technologies in the same box if you wish, but you would have to provide multiple DACs as well, to convert the digital signal channels from the digital crossovers to feed the analogue Class D amplifiers. There is no correlation between DSP and Class D amps.

I look forward to the Focal / Naim partnership bringing out a range of active digital speakers to show how it can be done for domestic use at hopefully a reasonable price.

A clean and efficient solution. No need for DACs, speaker cables, amps - what will we talk about?

Loudspeakers must always contain an analogue tranducer, that's how they work, - your ears are analogue. If you provide a digital signal source, then you must use a DAC to drive the analogue transducer.

JC

Jc,

Not so. Class D amps switch their output drivers at high frequency, varying the on / off duty cycle. The binary waveform used to control these drivers can be derived from an analogue input signal as you suggest, or it can be derived directly from a digital source such as SPDIF using DSP techniques. So no DAC required, it is implicit in the output drive topology.

Check out 'class d' on Wikipedia.

 

[jcbrum]

andyjm,

I am fully familiar with the paragraph on Wikipedia to which you refer. It is simply a description of an input circuit which comprises an alternative form of a digital to analogue converter, - otherwise known as a DAC.

I suggest you study a rather more authoritative work on electronic theory, rather than Wikipedia.

I assure you that Class D amplifiers are, fundamentally, analogue devices,

JC

 

[nopiano]

If you include the Devialet, then I'd say I've never heard better. Different, maybe, but not better.

http://www.whathifi.com/review/d-premier

Interesting, you have heard the Devialet D Premier. Can you tell me where you heard it, and what it sounded like (plus describe the rest of the system etc). From what I have seen and read that looks like the perfect marriage of Class A and Class D and I would love one, or at least a cheaper version of one.

only six months later...

I heard it at Oxford Audio Consultants, where my Krell and Sfs came from. Have listened via Sonus fabers and KEF Blades. Hard to ascribe a character at all. To my ears it was simply wide-open and super clean, but without lacking "emotion". And it is slim, and has a great remote volume rotary control.

 

[andyjm]

andyjm,

I am fully familiar with the paragraph on Wikipedia to which you refer. It is simply a description of an input circuit which comprises an alternative form of a digital to analogue converter, - otherwise known as a DAC.

I suggest you study a rather more authoritative work on electronic theory, rather than Wikipedia.

I assure you that Class D amplifiers are, fundamentally, analogue devices,

JC

OK, so which part of an amp that takes a PCM input, converts it to a modulated bitstream using DSP techniques, and then uses that bitstream to switch the output drivers on and off is fundamentally analogue?

Perhaps if you could post a link to the authoritative work on electronic theory you mention, that may help me understand.

In the meantime, have a look at NAD's white paper on their 'M2' direct digital drive class D amp.

 

[jcbrum]

Any good Degree level electronic theory textbook will explain the working conditions of Class D amplifiers, they're nothing new, - do your own homework.

Audio manufacturers' 'White Papers' are mostly a joke, they're mostly an extension of their advertising and promotions department, I don't suggest you take them very seriously.

JC

 

[andyjm]

Any good Degree level electronic theory textbook will explain the working conditions of Class D amplifiers, they're nothing new, - do your own homework.

Audio manufacturers' 'White Papers' are mostly a joke, they're mostly an extension of their advertising and promotions department, I don't suggest you take them very seriously.

JC

Hmmn. Perhaps you will take semiconductor manufacturer data sheets seriously, or are they also an extension of the advertising department?

To save you doing any homework, the link below is to the DIodes Inc. Direct Digital Feedback Amplifier (DDFA) chipset used in the NAD amplifier, which goes to explain in some detail how the class D output drivers are driven direct from the digital input with no intermediate analogue steps.

http://www.diodes.com/_files/free_pages/u_0_lnk_090413235508.pdf

Just to clarify an earlier point, a class D digital amp clearly acts as a DAC - it has a digital input, and drives an analogue tranducer, the point is the whole amp is the DAC, there is no internal DAC turning the digital input into an analogue signal to drive the output stages.

 

[dumbledore]

My feeling is that this technology needs to be perfected before it takes over from classical amplifiers. The fact that the final stage is the DAC is good in principle as the signal is not degraded in various anlaogue pre amplifier stages. However, we all know how DAC is critical for the sound quality. Doing the DAC stage at the output stage is certainly tricky and there should still be a lot of technical challanges to perfect this process to optimise sound quality. The other problem with this technology is that if is perfected it will not allow amplifier manufacturers to make the amplifier sound in certain way as all amplifiers will sound the same.

 

[jcbrum]

. . . the point is the whole amp is the DAC, there is no internal DAC turning the digital input into an analogue signal to drive the output stages.

Well this is where we'll have to disagree.

Fundamentally a Class D audio amplfier is simply a pulse-width modulated power amplifier with the pulse modulated by the audio signal.

You can fit a fancy front end to it which is simply a digital to analogue converter stage to achieve the audio modulation of the PWM output stage.

The whole point of a Class D amplifier is to operate the output transistors by turning them either fully on or fully off, with effectively no in-between state, so that no power is dissipated internally by the output devices. That is how the efficiency and low heat dissipation of Class D is acheived. This is accomplished by switching them at a high frequency (compared to audio) of something in the order of 250kHz. The width (in the time domain) of the hf pulses is modulated by the analogue audio waveform desired as the output signal, used to drive the analogue transducers in the loudspeakers.

You can't listen to digits, whether they be PCM or s/pdif, or any other digital stream, and expect to hear music. You have to use a converter stage to produce the required analogue signal which is the desired music. Some Class D designs incorporate this converter stage as you describe. It's still a form of DAC, the output of which is used to modulate the PWM output stage, which is the part that is operating in Class D.

A Class D amplifier is a bit like a powerful switch-mode power supply which is modulated by the analogue audio signal desired at the output, which is then used to energise the loudspeaker coil.

You can't listen to digits. If you've got no converter stage, you've got no music.

JC

 

[andyjm]

Well this is where we'll have to disagree.

You have to use a converter stage to produce the required analogue signal which is the desired music. Some Class D designs incorporate this converter stage as you describe. It's still a form of DAC, the output of which is used to modulate the PWM output stage, which is the part that is operating in Class D.

JC

I think we do now generally agree on the innards of a 'full digital' class D amp. My point remains that there are no analogue steps in the amplifier, the input PCM signal gets turned into a PWM signal that then drives the output stages. The only point at which the signal becomes 'analogue' is after the passive low pass filter on the amplifier output.

Where we disagree is to call that 'fundamentally analogue'. To me that looks 'fundamentally digital'.

 

[CnoEvil]

For the electronically inept, are all Class D amps created equal?

In other words are there two types - ie. some that are basically analogue with a switchmode power supply, while others are digital right the way through till it gets to the speakers?

If the above is the case, which is likely to give the better result?.......thinking aloud, I would have thought keeping things in the digital domain as long as possible seems to make sense.

 

[dumbledore]

Looking at the wikipedia page start to feel a bit more unconfortable with the technology. It looks like staying digital untill the end is not a practical proposition as feedback cannot be applied using conventional analogue techniques. (perhaps digital feedback is possible though at a cost). Feedback seems to be needed in order to iron out impedance matching of the load (speakers) which can result in nonlinear response. Can't see with all the limitation this technology is displaying how class D will be succesful in a HIFI environment. Can only think they will be OK in a night club where power is the main requirement.

 

[CnoEvil]

Looking at the wikipedia page start to feel a bit more unconfortable with the technology. It looks like staying digital untill the end is not a practical proposition as feedback cannot be applied using conventional analogue techniques. (perhaps digital feedback is possible though at a cost). Feedback seems to be needed in order to iron out impedance matching of the load (speakers) which can result in nonlinear response. Can't see with all the limitation this technology is displaying how class D will be succesful in a HIFI environment. Can only think they will be OK in a night club where power is the main requirement.

I'm not a particular fan of Class D, but there are interesting products out there from the likes of Nad, Bel Canto, Primare and Devialet. Due to the green issues with Class AB etc, there is more effort being put into this type of design.